An unprecedented [5 + 2 + 1] cascade cyclization to the preparation of 5H-pyrimido­[5,4-b]­indole derivatives has been disclosed. The novel protocol of 2-nitrochalcones reacted with aliphatic primary amines catalyzed by CuI and promoted by Cs2CO3, which underwent a critical intermediate 2,3-disubstituted indole, providing structurally diverse 5H-pyrimido­[5,4-b]­indoles in generally high yields (77–90%) and broad substrate scopes (34 examples).

In this report, a practical synthetic approach to access N-aryl/N-alkyl 4-pyridones via a two-step continuous flow process has been developed. In comparison to batch conditions, this [3 + 2 + 1] cycloaddition involving a threecomponents cascade reaction of aniline, dialkyl ethoxymethyl enemalonate and dialkyl acetylenedicarboxylate under mild conditions, which can provide N-aryl/N-alkyl 4-pyridone derivatives with a wider substrate scope and good to excellent yields.

In this study, a concise and efficient protocol for the construction of diverse cyclohexanedione-fused 2,8oxaza/2,8-dioxa bicyclo[3.3.1]nonanes and 4-substituted 4Hchromenes between 2-hydroxychalcones and 3-aminocyclohex-2-enones has been accomplished. This switchable syn-thesis concerning the three types of functionalized heterocyclics via tunability of the deamination/dehydration process was controlled by Brønsted acid catalyst or solvent effects in this cascade transformation, which can thus provide the desired products in good to excellent yields.